Currently, researches and commercialization of a point of care (POC) and a lab-on-a-chip (LOC) (which means a laboratory on a chip and is a technology for diagnosing various diseases in a small chip at a time) are actively carried out in a bio-industry. Typically, products allowing for a rapid diagnosis and experiment as the POC or LOC are released as a product with a special surface treatment or reagent fixed in a plastic micro chip or cartridge. It can be said that the cartridge or chip is a core of the product.
Generally, the plastic micro chip or cartridge used for the POC and LOC is made of polyethylene (PE) derivatives such as polycarbonate (PC), polystyrene (PS), polypropylene (PP) and polyethyleneterephthalate (PET), polymethylmethacrylate (PMAA) or an acryl based plastic, and is used as a disposable.
FIGS. 1 and 2 show a typical plastic micro chip used for a lab-on-a-chip. Generally, the plastic micro chip comprises an upper substrate 16, a lower substrate 18 and a sample filling space (channel) 10 having a predetermined height D or a fine structure, etc. between the upper and lower substrates.
It is required that the channel should be precisely manufactured to have a height of several μm to several hundreds μm when manufacturing the plastic micro chip. Accordingly, it is required to very precisely and correctly bond the upper and lower substrates including the channel or fine structure so that the plastic micro chip can perfectly function. In addition, surface properties of main parts of the cartridge or the chip should be maintained as they are.
When manufacturing the plastic micro chip, the upper and lower substrates are generally bonded by a heat bonding, an ultrasonic bonding, an optical method or an adhesive using a primer.
The heat bonding method is mainly used to bond the material such as a film. The optical method is a boding method using a specific molecular structure of the plastic surface and can be applied to some plastics only. The method using the adhesive is used even in daily life. The ultrasonic bonding method is actively used in industries.
However, there are some disadvantages when bonding the plastic micro chip using the above methods. In other words, there is a limitation in correctly and precisely bonding the chip having the fine channel or structure without an error, and it is difficult to bond the chip without influencing on properties of an inner surface thereof.
FIGS. 3 and 4 show a bonding process according to an ultrasonic bonding method of the prior art.
As shown in FIG. 3, a protrusion is formed on a lower surface of an upper substrate 16 and a recess is formed in an upper surface of a lower substrate 18. Then, when an ultrasonic wave is applied with the upper and lower substrates 16, 18 being overlapped, the protrusion of the upper substrate 16 is melted and thus the upper substrate 16 is bonded to the lower substrate 18. However, as shown in FIG. 4, since the bonding surface is irregular and rough, an empty space can be formed and it is difficult to control the channel to have a predetermined height (D), so that an error can occur.
Generally, in a plastic micro chip, the height of the channel should be also precisely controlled in order to precisely manufacture a volume of the channel. However, it is difficult to precisely control the height of the channel with the prior bonding methods.
In addition, since the channel is not completely sealed and an empty space can be thus formed, a sample in the channel can flow out to the exterior and an air bubble can occur in the sample inside of the channel.